A connecting device with the aforementioned features is described in EP 0 366 789 B1. On both sides the end areas of pipes to be connected to each other are pushed into corresponding receptacles of a connecting body. These end areas of the pipes are each provided with a radial tube bulge on each of which a union nut is supported to fasten the assigned pipe end on the connecting body. The union nuts can be screwed onto corresponding external threads provided on the connecting body so that when assembling the connecting device the pipe ends are pressed into and held fast in the receptacles provided on the connecting body. If in terms of the correct or stipulated assembly of the connecting device it depends on the union nuts being screwed into the correct position on the connecting body in order to ensure pre-tensioning between the connecting body, the union nut and the pipe end that is sufficient for the tightness of the connecting device, between the end faces of the union nut and connecting body disc springs with a coloured surface are arranged. If the end faces of the union nut and connecting body are at an axial distance before assembly, this distance is bridged by the disc spring, supported between the end faces of the union nut and connecting body, which at the start of assembly is arranged obliquely between the separate end faces so that its coloured surface can be seen. With increasing screwing of the union nut onto the connecting body the disc spring is tensioned and steepens so that at the end of assembly only the outer circumferential surface of the disc spring, which is not coloured, remains visible. In this way the assembly status can be identified.
Associated with the known assembly marking in the connecting device described in EP 0 366 789 B1 is the drawback that depending on the tolerance situation or the assembly conditions in repeated dismantling and assembly of the connecting device, the disc springs used give way more quickly and can even been pressed flat without there be sufficient pre-tensioning between the components to ensure tightness. Another possibility consists in sufficient pre-tensioning already being present at a certain position of the union nut, but the disc spring not yet being pressed fully flat, so that in spite of reaching the end assembly position the disc spring in question identifies the assembly status as not being sufficient.